When a desired product is produced using yeast (Saccharomyces cerevisiae) or the like, a yeast mutant is prepared by gene introduction in a manner such that a gene involved in the biosynthesis of the desired product can be constitutively expressed in the yeast mutant, the yeast mutant is cultured under adequate culture conditions, and the desired product is collected inside or outside the cultured cells. In addition, when a desired product is a non-ethanol substance, it is preferable to reduce large amounts of produced ethanol. Hitherto, in order to reduce ethanol production capacity, gene disruptants from the pyruvate decarboxylase gene and the alcohol dehydrogenase gene involved in the ethanol production pathway have been prepared. However, particularly in the case of a bacterium exhibiting the Crabtree effect, such as Saccharomyces cerevisiae, proliferation or fermentation capacity significantly decreases while the amount of ethanol produced decreases, resulting in poor practical usefulness, which has been problematic (Non-Patent Document 1: Ishida, N. et al. (2006) Biosci. Biotechnol. Biochem., 70, pp. 1148-1153; Non-Patent Document 2: Flikweert, M. T. et al. (1996) Yeast 12, pp. 247-257; Non-Patent Document 3: Eri, A. et al. (1998) J. Ferment. Bioeng., 86, pp. 284-289; Patent Document 1: JP Patent Publication (Kohyo) No. 2003-500062 A; Patent Document 2: JP Patent Publication (Kohyo) No. 2001-516584 A; and Non-Patent Document 4: Skory, C. D. (2003) J. Ind. Microbiol. Biotechnol., 30, pp. 22-27). In addition, according to Non-Patent Documents 1, 3, and 4, ethanol can be significantly reduced by disrupting the genes involved in the ethanol production pathway. However, it is not always possible for the greatest portion of a product formed as a result of reduction of ethanol to be obtained in the form of a desired product.
Meanwhile, it has been reported that the yield of a desired product can be improved by partially blocking the ethanol production pathway so as to promote the metabolic pathway of the desired product (Non-Patent Document 5: Saitoh, S (2005) Appl. Environ. Microbiol., 71, pp. 2789-2792). However, in such case, although the yield of the desired product can be improved, ethanol reduction is insufficient and the fermentation rate decreases slightly, which is problematic.    Patent Document 1: JP Patent Publication (Kohyo) No. 2003-500062 A    Patent Document 1: JP Patent Publication (Kohyo) No. 2001-516584 A    Non-Patent Document 1: Ishida, N. et al. (2006) Biosci. Biotechnol. Biochem., 70, pp. 1148-1153    Non-Patent Document 2: Flikweert, M. T. et al. (1996) Yeast 12, pp. 247-257    Non-Patent Document 3: Eri, A. et al. (1998) J. Ferment. Bioeng., 86, pp. 284-289    Non-Patent Document 4: Skory, C. D. (2003) J. Ind. Microbiol. Biotechnol., 30, pp. 22-27    Non-Patent Document 5: Saitoh, S (2005) Appl. Environ. Microbiol., 71, pp. 2789-2792